More than 500 Scout groups could close and others face a "bleak" future with coronavirus hampering fundraising, the Scout Association has said.
Groups in some of the poorest areas of England were hit when social distancing ended jumble sales, quizzes and car washes, the organisation said.
But a new fundraising campaign aims to try to save those most at risk, with a virtual race around the world.
Chief Scout Bear Grylls said scouting was needed now more than ever.
More than 7,000 groups have so far joined the fundraising event, which challenges Scouts to travel 172,000 miles collectively in their local areas.
The campaign hopes to raise £300,000 for the various groups at risk of closure, the association said.
Groups in areas including Pontefract and Castleford in West Yorkshire, Birkenhead, Wolverhampton, Norfolk, Greater Manchester, Greater London, East Sussex, the Isle of Wight, Kent and Shropshire are also at risk of closure, the association said.
What do Scouts do?
- According to founder Robert Baden-Powell, "a Scout is a friend to all" and is encouraged to be kind and "do their best" for themselves and others
- He wanted to bring young people from different backgrounds together and organised a camping and fishing trip in Dorset for about 20 boys in 1907
- That led to ten of thousands of boys, usually aged 10 and 11, going on to become Scouts all over the UK and taking part in activities like camping, hiking and abseiling
- From the age of six, children can join the Beavers and go on to Cubs from the age of eight. After turning 14, teenagers can move on from Scouts to Explorers and Network up to the age of 25
- Girls have been members of the Scout Association for over 40 years and, aside from outdoor activities, the association says youngsters will also learn vital life skills as individuals and being part of a team
- More than 800 groups have opened in deprived areas since 2013 and member numbers have risen year on year with more than 400,000 people aged between six and 18 in the movement in 2018
"As Scouts we always support each other and in today's tough climate, where we all need inspiration and community, we are taking part all together in our Race Round the World," Grylls said.
"Scouting plays a fundamental role in the lives of thousands of young people, giving them skills and hope for the future.
"That is now more vital than ever. I am so proud of those doing their mile in support of those hit hardest by the Covid-19 pandemic."
The majority of groups were now "back up and running", the association added.
Last year, the association said more than 60,000 children were on waiting lists to become Scouts, Beavers, Cubs or Explorers, an increase of 20% over the past three years.